ß-thalassemia intermedia is a disorder characterized by ineffective erythropoiesis (IE), anemia, splenomegaly and systemic iron overload. Novel approaches are being explored based on the modulation of pathways that reduce iron absorption (i.e. using hepcidin activators like Tmprss6-antisense oligonucleotides (ASO)) or increase erythropoiesis (by erythropoietin (EPO) administration or by modulating the ability of transferrin receptor 2 (Tfr2) to control red blood cell (RBC) synthesis). Targeting Tmprss6 mRNA by Tmprss6-ASO was proven to be effective in improving the IE and splenomegaly by inducing iron restriction. However we postulated that combinatorial strategies might be superior to single therapies. Here we combined Tmprss6-ASO with EPO administration or removal of a single Tfr2 allele in the bone marrow of animals affected by ß-thalassemia intermedia (Hbbth3/+). EPO administration alone or removal of a single Tfr2 allele increased hemoglobin levels and RBCs. However, EPO or Tfr2 single allele deletion alone, respectively, exacerbated or did not improve the splenomegaly in ß-thalassemic mice. To overcome this issue, we postulated that some level of iron restriction (by targeting Tmprss6) would improve the splenomegaly while preserving the beneficial effects on RBC production mediated by EPO or Tfr2 deletion. While administration of Tmprss6-ASO alone improved the anemia, combination of Tmprss6-ASO+EPO or Tmprss6-ASO+Tfr2 single allele deletion showed significantly higher hemoglobin levels as well as reduction of splenomegaly. In conclusion, our results clearly indicate that these combinatorial approaches are superior to single treatments in ameliorating the IE and anemia in ß-thalassemia and could provide guidance to translate some of these approaches into viable therapies.

The Nuclear Receptor Coactivator 4 (NCOA4) promotes ferritin degradation and Ncoa4-ko mice in C57BL/6 background show microcytosis and mild anemia, aggravated by iron deficiency. To understand tissue specific contribution of NCOA4-mediated ferritinophagy we explored the effect of Ncoa4 genetic ablation in the iron-rich strain Sv129/J. Increased body iron content protects mice from anemia and, in basal conditions, Sv129/J Ncoa4-ko mice show only microcytosis; nevertheless, when fed a low-iron diet they develop a more severe anemia compared to wild-type animals. Reciprocal bone marrow (BM) transplantation from wild-type donors into Ncoa4-ko and from Ncoa4-ko into wild-type mice revealed that microcytosis and susceptibility to iron deficiency anemia depend on BM-derived cells. Erythropoiesis reconstitution with RBC count and hemoglobin normalization occurred at the same rate in transplanted animals independently of the genotype. Importantly, NCOA4 loss did not affect terminal erythropoiesis in iron deficiency, both in total and specific BM Ncoa4-ko animals compared to controls. On the contrary, upon a low iron diet, spleen from wild-type animals with Ncoa4-ko BM displayed marked iron retention compared to (wild-type BM) controls, indicating defective macrophage iron release in the former. Thus, EPO administration failed to mobilize iron from stores in Ncoa4-ko animals. Furthermore, Ncoa4 inactivation in thalassemic mice did not worsen the hematological phenotype. Overall our data reveal a major role for NCOA4-mediated ferritinophagy in macrophages to favor iron release for erythropoiesis, especially in iron deficiency.

β-thalassemia is a genetic disorder caused by mutations in the β-globin gene, and characterized by anemia, ineffective erythropoiesis and iron overload. Patients affected by the most severe transfusion-dependent form of the disease (TDT) require lifelong blood transfusions and iron chelation therapy, a symptomatic treatment associated with several complications.Other therapeutic opportunities are available, but none is fully effective and/or applicable to all patients, calling for the identification of novel strategies. Transferrin receptor 2 (TFR2) balances red blood cells production according to iron availability, being an activator of the iron-regulatory hormone hepcidin in the liver and a modulator of erythropoietin signaling in erythroid cells. Selective Tfr2 deletion in the BM improves anemia and iron-overload in non-TDT mice, both as a monotherapy and, even more strikingly, in combination with ironrestricting approaches. However, whether Tfr2 targeting might represent a therapeutic option for TDT has never been investigated so far. Here, we prove that BM Tfr2 deletion improves anemia, erythrocytes morphology and ineffective erythropoiesis in the Hbb th1/th2 murine model of TDT. This effect is associated with a decrease in the expression of α-globin, which partially corrects the unbalance with β-globin chains and limits the precipitation of misfolded hemoglobin, and with a decrease in the activation of unfolded protein response. Remarkably, BM Tfr2 deletion is also sufficient to avoid long-term blood transfusions required for survival of Hbb th1/th2 animals, preventing mortality due to chronic anemia and reducing transfusion-associated complications, such as progressive iron-loading. Altogether, TFR2 targeting might represent a promising therapeutic option also for TDT.